Hyaluronic acid (HA), which can be crosslinked, and collagens are biomaterials used in the fields of surgery and dermatology as fillers to recontour/reconstruct tissues. The market of cosmetic fillers for soft tissue augmentation has increased in recent years and there is a need to create longer lasting materials that are retained at the site of application. Physicians also would like to improve control over the final result and allow for subsequent correction to optimize patient satisfaction.
Hydrogels hold the promise of creating dermal fillers that maintain aesthetic corrections longer than currently available fillers. The term, “hydrogel,” refers to a broad class of polymeric materials that contain water but do not dissolve in water. Generally hydrogels are cross-linked and networked polymer chains. If there are two or more crosslinks per polymer chain, a network is formed that is able to absorb large amounts of solvent. Hydrogels are of particular interest in the field of tissue engineering because of their tissue-like water content, which allows nutrient and waste transport.
There are a number of methods to form polymers and to crosslink polymers. One such method involves light-reactive reagents and light-induced reactions which create reactive species in a monomer solution, wherein the monomers are polymerized to form chains, monomers, polymers and chains, which in turn can form networks.
Currently used cosmetic fillers are generally derived from biological polymers, such as collagen or hyaluronic acid. Since these compounds are biological in nature, they tend to be sensitive to degradation even if crosslinked. Hence, the esthetic duration of an enhancement/correction achieved with such materials is limited in time, and frequently requires the recipient to undergo additional and expensive repeat injections/treatments to maintain a desired effect. Another drawback of conventional cosmetic fillers is the lack of malleability and contourability to maintain a desired and/or corrective formation after injection, such as, for example, in human cheek bone or chin manipulations. Thus, for these types of and other similar procedures, a more invasive approach is used wherein plastic implants are inserted while a patient is under general anesthesia. Hence, a need continues to exist in the cosmetic reconstructive arts for improved polymeric fillers that are contourable and longer lasting.
Synthetic polymers have highly controllable physical and degradation properties, making them suitable for creating an implant with specific properties. Poly(ethylene glycol), PEG, is an example of a frequently used biocompatible synthetic polymer. PEG, and other synthetic polymers, can be modified to react with functional groups to allow crosslinking and to form hydrogels.
A PEG derivative, poly(ethylene oxide) diacrylate (PEODA), can be injected into the body as a solution and can be polymerized to form a crosslinked, insoluble gel [1-5]. To induce photopolymerization by free radical formation, various photoinitiators have been used. In particular, Hubbell and his colleagues previously created PEODA hydrogels using Eosin Y/triethylamine via argon ion laser (514 nm, 70 mW/cm2, 2 s exposure; American Laser, Salt Lake City) [6]. Eosin Y is a good candidate as a transdermal photoinitiator because of its adsorption range in visible blue light [7,8]. The advantage of visible light, as compared to UV, is that the longer visible wavelength can penetrate deeper into the skin. Moreover, high doses of UV light have been implicated as a cause for erythema and different types of skin cancers [9]. Therefore, photopolymerization using a visible light source would be suitable for the proposed cosmetic applications. Feasibility of PEODA photopolymerization with visible light using Eosin Y as the initiator under human skin, however, is yet to have been established.
Intense pulsed light (IPL) devices are a common visible light source in a dermatology office for photorejuvenation and photoepilation procedures [10-13]. The compatibility of Eosin Y photoinitiation with an IPL device, however, has not been established.
These and other deficiencies in the art of cosmetically useful preparations are satisfied with the present invention.